The present invention relates to refrigeration systems in general, and more particularly to refrigeration systems which provide cooling for air as well as machinery fluids.
Many industrial processes require control of the temperature of the material being processed and often of the machines handling the material. Particularly in the food industry an entire plant may be cooled to prevent spoilage and the growth of bacteria in foodstuffs. This is particularly a concern with meat, where it is important to control bacterial growth to assure product safety.
In an industrial setting, ammonia is oft en employed as a refrigerant. Ammonia is low cost and an efficient refrigerant for the temperature range of interest in many industrial processes. The hazards associated with ammonia: namely, flammability and toxicity if inhaled, are safely handled in an industrial setting where safety practices and monitoring equipment can be reliably employed. Thus, for industrial processes, ammonia is one of the most widely used refrigerants.
Ethylene glycol is a widely used coolant. When used alone or mixed with water it has excellent heat absorbing characteristics, good thermal conductivity, and remains liquid over a broad temperature band. Whereas ammonia is used in a refrigerator or heat pump to transport heat energy from a cool reservoir to a warm reservoir, ethylene glycol transports heat from a warm reservoir to a cool reservoir.
In industrial plants, merely keeping the air at a desired temperature will not typically ensure that a material being handled within the plant remains near the air temperature. Machines which perform work convert energy stored as hydraulic pressure into mechanical motion. Most of the energy, however, is eventually converted into heat. Where a material is worked by a machine, the machine and the material may become undesirably heated. For machines employing hydraulic fluid to transfer energy, a typical process is to cool the hydraulic oil used by individual machines by passing water through a heat exchanger so that heat from the oil is given up to the cooling water.
Ground water is sometimes used as a low cost source of cooling fluid to extract heat from hydraulic oil. Water has a high specific heat and when pumped from below the ground typically has a temperature, determined principally by latitude, which in the Midwest is typically in the neighborhood of 55 degrees Fahrenheit. In the past this ground water could be obtained at the cost of pumping it from the ground.
Modern industrial plants, particularly those handling organic material, are typically connected to their own or to a municipal sewage treatment plant. Particularly when connected to a municipal sewage treatment plant, the cost of treatment is based on the amount of water consumed. Thus the use of an open loop water cooling system can have considerable negative economic consequences.
To address this problem, a closed loop cooling system was developed. In this system, which is set forth in pending U.S. patent application Ser. No. 09/443,604, filed Nov. 19, 1999, the disclosure of which is incorporated by reference herein, refrigerant used in providing air conditioning to a plant is also used to remove heat from a coolant, typically ethylene glycol, by use of a first heat exchanger. The coolant is circulated through via a supply header to a plurality of individual machine cooling loops, where it passes through a heat exchanger to cool machine hydraulic fluid. After passing through the individual heat exchanger for each machine, the coolant fluid from the individual machine cooling loops passes into a fluid return header, from where it is pumped to the first heat exchanger for the cycle to begin again.
While this system is very efficient, it fails to address undesirable machine heating that may occur with respect to machine fluids other than hydraulic fluid. For example, many machines, in addition to hydraulic systems, also involve gears to transfer energy. Such gears, which are usually contained in a gear box on the machine, are lubricated by gear oil to reduce heat and friction. Such lubrication is desirable, because both heat and friction adversely affect the gears, and significantly reduce their useful life.
As machines are operated at higher speeds, the gears move at a faster rate, thus generating increased amounts of friction and heat. This, in turn, results in the temperature of the gear lubricating oil rising to undesirably high levels, which if maintained over time will result in accelerated wearing of the gears themselves. To prevent high gear oil temperatures from occurring, the simple solution is to operate the machines at a reduced speed such that the gear oil temperature remains within a specified recommended range. However, this solution results in decreased machine efficiency and productivity.
Accordingly, there is a need to keep additional machine fluids besides hydraulic fluid within a temperature range sufficient to avoid excess wear and tear to machine components, such as gears. There is also a need to maintain such fluids within such a temperature range even when the machine is operating at high rates of speed. Moreover, there is a need to accomplish the above in an efficient and effective manner.
The cooling system of this invention employs a coolant transport loop which is cooled by the existing plant ammonia-based air conditioning or other refrigeration system. The coolant loop, which employs a liquid coolant, moves through an ammonia evaporator where the coolant is lowered to a set point temperature, typically around 50 degrees Fahrenheit. The coolant then flows to a supply header.
The supply header is connected to a return side header by one or more individual machine cooling loops which pass through one or more associated heat exchangers mounted on individual machines for cooling the fluids employed by each machine, including hydraulic fluid and gear oil. In this regard, a single combination-type heat exchanger capable of cooling two or more separate fluids can be used for each individual cooling loop. Multiple heat exchangers, one for each fluid, can also be used, and can be aligned in series or in parallel. The return header is connected through an isolation valve to a surge tank and to a pump that returns the fluid to the ammonia heat exchangers where the coolant, typically ethylene glycol or an ethylene glycol/water solution, is again cooled and sent to the supply header.
It is an object of the present invention to provide a lower cost method of cooling industrial machinery.
It is a further object of the present invention to provide a method of regulating the cooling of a plurality of machines without introducing ammonia into the factory floor.
It is a still further object of the present invention to eliminate open loop cooling within a manufacturing facility handling foodstuffs.
It is yet an additional object of the present invention to provide an efficient and effective system for cooling at least two machine fluids in a given machine.
It is another object of the present invention to provide a system for extending the life of machine parts serviced by such fluids.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.